The present invention relates to a container, which comprises a venting means.
The problem of container deformation in response to pressure differences existing between the inside of a closed container and the ambient pressure is well known in the packaging industry. Such container deformation may be non-recoverable for certain container materials, like some plastics or metals. Thin-walled, partially flexible containers are particularly sensitive to the problem.
There are a number of possible factors which may lead to the existence of the pressure differences between the interior and the exterior of the container mentioned above. The content of the container may, for example, be chemically unstable or may be subject to reaction with gases which may exist in the head space of the container, or alternatively, in certain specific circumstances, may react with the container material itself. Any chemical reactions involving the liquid contents may lead to either production of gases, and hence to over-pressure in the container, or to the absorption of any head space gases thereby causing under-pressure in the container.
Pressure differences between the pressure inside the container and the ambient atmospheric pressure may also occur when the temperature during the filling and sealing of the container is significantly different from external temperature during shipment, transportation and storage. Another possibility of a pressure difference may be caused by a different ambient pressure at the filling of the container from another ambient pressure at a different geographical location.
The prior art has proposed several solutions using valve systems which avoid pressure differences between the interior and the exterior of the container. Proposed solutions also relate to various venting caps which allow pressure generated inside the container to be released by escape of gas. For example, FR-A-2,259,026, U.S. Pat. No. 4,136,796 and DE-A-2,509,258 disclose self-venting closures comprising a gas-permeable membrane covering an orifice to the exterior. The membranes are made of a material which is impermeable to liquids, but permeable to gases. Therefore, containers may comprise apertures to release gas to the exterior without losing their leak-tightness. Another example is EP-A-593,840 which discloses containers for containing liquids which generate pressure, the container being made of a thermoplastic material comprising a network of micro-channels. This network of micro-channels is permeable to gases, but not to liquids.
It has been found that should liquid product contact these membranes, or the extremity of micro-channels, the membranes may lose at least part of their gas-permeability. Specifically, liquid products comprising particulate solids such as carbonate and/or percarbonate and/or perborate suspended in the liquid product may not completely drain away from the membrane back into the container. Instead it has been found that the pores of the membrane are clogged by these particulate solids sedimented out of the liquid. In this manner, it may happen that the container loses venting capacity. This loss of venting capacity results in a pressure difference between the exterior and the inside of the container which may deform the container.
The contact between the product and the membrane may be caused by splashes of the product onto the membrane as the filled container is agitated during shipment and transportation of the container. It has been found that the amount of splashes normally occurring during shipment and transportation are sufficient to completely interrupt the venting capacity of the container. Another means by which product may contact with the membrane is during an upside down storage of the container. It has been further found that other venting systems, like valves for example, may also suffer from a similar disadvantage.
As mentioned before, an important parameter which influences the venting capacity of the membrane is that the product which has contacted the membrane may sediment out some particulate solids suspended in the product. It is therefore an object of the present invention to provide a container containing a liquid product, the liquid product comprising particulate solids, the container allowing venting of the product by venting means, whereby the sedimentation of the particulate solids from the liquid product onto the venting means is substantially reduced.
The present invention provides a container containing a liquid product. The container enables the venting of the liquid product by a venting means. The venting means allows the passage of gases between the interior and the exterior of the container when the pressure inside the container differs from the ambient pressure. The venting means is permeable to gases, but impermeable to the liquid product. The liquid product comprises particulate solids selected from the group consisting of carbonate, percarbonate, perborate and mixtures thereof. The size of the particulate solids is not greater than 400 xcexcm.